Yersinia enterocolitica is a Gram-negative pathogen responsible for a range of clinical syndromes but is primarily associated with gastrointestinal disorders. A number of important paradigms of pathogenesis have emerged from the studies of Y. enterocolitica and Y. pseudotuberculosis. In addition these enteropathogens have served as important models of bacterial invasion, a process primarily encoded by inv. Virulence properties such as invasion can be characterized at the molecular level due to the ease of manipulation of these bacteria in the laboratory and the existence of an excellent murine model of infection for dissecting the host-pathogen interaction. In studies to further our knowledge of inv and its role in virulence we identified a gene, rovA, that regulates expression of inv both in the laboratory and during infection. Subsequent studies demonstrated that RovA acts as a DNA binding protein and promotes inv expression by displacing a repressor complex from the inv promoter. The rovA mutant was less virulent than either the wild type strain or the inv mutant. The rovA virulence defect is characterized by reduced systemic dissemination and an increased LD50 after oral infection. Infection using the i.p. route abrogates the rovA defect, suggesting RovA is required for events occurring either in/from the intestine/colon or in the Peyer's patch. Because the rovA mutant virulence defect was more significant than that of an inv mutant alone, this suggested RovA regulates additional virulence determinants. However, RovA did not appear to regulate the expression of previously identified virulence determinants. Using whole genome microarray analysis we identified 64 genes potentially regulated by RovA, suggesting the regulon may be quite large. The long-term goals are (i) to understand how these genes are regulated by RovA and how that is coordinated with expression of other virulence factors, and (ii) to determine which RovA regulated genes (rrg) contribute to virulence. Specifically we propose the following: (Aim 1) What is the role of the RovA regulon during infection? Recently our understanding of how enteric pathogens interact with the intestinal mucosa and spread systemically has changed significantly but questions still remain. In addition, questions regarding how these bacteria spread from host-to-host are more tractable. Given the known virulence defects of the rovA mutant, we hypothesize that the RovA regulon will play a role in these host-pathogen interactions and feel that a more detailed understanding of both wild type and the rovA mutant with respect to these aspects of infection is warranted. (Aim 2) Which rrgs are important for virulence and how do they contribute to individual RovA-associated phenotypes? (Aim 3) Are all rrgs regulated in the same way as inv? By knowing when and where these gene products are expressed combined with information regarding the phenotype of mutations in these genes we may be able to gain a better understanding of their function. PUBLIC HEALTH RELEVANCE: Gastrointestinal disease is a significant cause of morbidity and mortality in infants and of morbidity in adults. Our long-range goal is to gain a full understanding of the Yersinia enterocolitica virulence factors and their contribution to the disease process at the molecular level. This will expand our understanding and ability to intervene therapeutically not only with Yersinia but with many other gastrointestinal pathogens as well.